Viruses which integrate into the host cells genome and effect cellular metabolism have been investigated. Integration of the bacterial virus, lambda into the E. coli genome near the bacterial genes for galactose metabolism has been demonstrated under certain circumstances, to lead to gross discordinancy of the expression of the galactose metabolism genes. Virally induced discordinate gene expression was shown to be due an effect on the secondary structure of a messenger, RNA. The development of techniques to detect chromosomally integrated viral genomes, viral mRNA and virally altered metabolism in host cells has encouraged us to apply these technologies to investigate human diseases. The possibility of an association between a viral genome (integrated in the chromosome) and the occurrence of diseases inherited in a dominant manner, such as familial Alzheimer's disease is currently being examined. Integration of viral related nucleotide sequences in the genomic DNA of man will be studied using fibroblast cell lines established from individuals belonging to a family with histologically confirmed Alzheimer's disease.